If Mac keeps asking for login Password for Keychain

If you not sure of your old password

If you don't know your old password, the solution will be to create a new login keychain.

If you know what is your old password

If you know your old password, use that password to update your existing login keychain:

Step 1. 

Open the Keychain Access app, which is in the the Utilities folder of your Applications folder 

Step 2.

From the list of keychains on the left side of the window, select login 

Step 3. 

From the Edit menu in the menu bar, choose Change Password for Keychain login 

Step 4. 

Enter the old password of your user account in the Current Password field. This is the password you were using before the password was reset 

Step 5. 

Enter the new password of your user account in the New Password field. This is the password you're now using to log in to your Mac. Enter the same password in the Verify field 

Step 6.

Click OK when done, then quit Keychain Access.